Ok, I want to clear up a few things about fighting and dueling. Both are perfectly fine to do, but like all things, it must be practiced with moderation and common sense. You have to think of your surroundings before you fight. Obviously, if a fight broke out in the middle of a street, someone would of course step in to stop it. In that same vein, if you were to kill a NPC, then someone would come and arrest you. If you commit a series of crimes, then obviously you will become a target for ANBU. Obviously friendly duels can be held outside of the central village as well.

To leave the village limits for any reason other than a mission, you will need your Kage's permission, or you will be dubbed a missing nin, and be treated as such. Missing nin will obviously have troubles moving from village to village, and will be chased by other shinobi. To lose missing nin status, you must be accepted by the Kage of another village, effectively betraying your old village.